Polymer brushes as smart coatings for On-Chip electrochemical sensors

Functional polymer brushes have a tremendous interest for surface engineering, thanks to their stimuli-responsive behaviour, allowing applications in the fields of the development of switchable wettability/adhesion devices, controlled release devices and especially sensors. In this work [1], silicon substrates functionalized with an alkoxysilane-type initiator were used as substrates to grow polymer brushes using SI-ARGET ATRP (Atom transfer Radical Polymerization). Different brushes compositions were obtained usingdifferent feed ratios of the two monomers (2-hydroxyethyl methacrylate (HEMA) and 2-aminoethyl methacrylate hydrochloride (AMA)). Both homopolymer (PHEMA, PAMA) andcopolymer (PHEMA-co-PAMA 80:20, PHEMA-co-PAMA 50:50) brushes were investigated. Moreover, the effect of micropatterning (achieved by remote photocatalytic lithography [2]) on the brushes properties was also determined. Every step (Figure 1) of this grafting-from procedure was studied using electrochemical techniques, in particular electrochemical impedance spectroscopy (EIS) (Figure 2), demonstrating the great potential of these techniques for the investigation of such complex systems. The homogeneity and density of the initiator layer and of the resulting brushes, their composition and thickness,have been thoroughly investigated. Brushes with different loading of cationic groups could be differentiated through their marked reactions to an anionic redox probe (ferrocyanide). Noteworthy, the brushes were grown on silicon substrate which is an atypical electrode material due to its very poor electrochemical response. Grafted-from brushes allowed the reaction of ferrocyanide at the silicon surface, behaving as «tentacles» to capture the redox probe and keep it in proximity of the silicon surface. Micropatterning was found to significantly improve the electrochemical behavior of the system. The obtained results pave the way to the development of on-chip electrochemical devices and microsensors. Applications for drug-delivery and microfluidics can be envisaged as well. References [1] G. Panzarasa, G. Soliveri, V. Pifferi, J. Mater. Chem. C 4, 2016, pp 340–347. [2] G. Panzarasa, G. Soliveri, K. Sparnacci, S. Ardizzone, Chem. Commun. 51, 2015, pp 7313–7316. Figure 1. Scheme of the polymer brushes grafting-from and examples of devices. Figure 2. EIS spectra of the different devices.